Center pivot irrigation system

Abstract

An irrigation system is disclosed which includes a center pivot support having an elongated main water boom pivotally connected thereto which extends outwardly therefrom. An elongated corner span is pivotally connected at its inner end to the outer end of the main boom and is supported by a steerable drive tower. A span sensor is positioned on the corner span for sensing changes in shape of the corner span. A control connects the span sensor with the drive for driving the steerable drive tower and the motor on the last regular drive unit on the main water boom to adjust the speed thereof upon the span sensor sensing predetermined changes in the shape of the corner span.

I claim: 
     
       1. An irrigation system, comprising: a center pivot support structure;   an elongated main water boom, having inner and outer ends, pivoted at its inner end to said center pivot support structure and extending outwardly therefrom;   said main water boom comprising an elongated main water pipe supported upon a plurality of non-steerable drive towers which propel said main water pipe around said center pivot support structure;   said non-steerable drive towers including a last regular drive tower which is driven by an electric motor;   an elongated corner span, having inner and outer ends, pivotally connected at its said inner end to said outer end of said main boom;   said corner span comprising an elongated extension water pipe supported upon at least one steerable drive tower;   steering means for steering said steerable drive tower;   drive means for driving said steerable drive tower, including at least one variable speed motor;   guidance means for controlling said steering means so that said steerable drive tower is moved along a preselected path, as said main boom travels over the field to be irrigated, thereby causing said corner span to pivotally move with respect to said main boom to cause said corner span to pivotally extend out into corner areas of the field and pivotally retract therefrom as said main boom travels through the field;   a span sensor positioned on said corner span for monitoring shape changes of said corner span;   control means connecting said span sensor and said drive means for adjusting the speed of said steerable drive tower upon said span sensor sensing changes in shape of said corner span.   
     
     
       2. An irrigation system, comprising: a center pivot support structure;   an elongated main water boom, having inner and outer ends, pivoted at its inner end to said center pivot support structure and extending outwardly therefrom;   said main water boom comprising an elongated main water pipe supported upon a plurality of non-steerable drive towers which propel said main water pipe around said center pivot support structure;   said non-steerable drive towers including a last regular drive tower which is driven by an electric motor;   an elongated corner span, having inner and outer ends, pivotally connected at its said inner end to said outer end of said main boom;   said corner span comprising an elongated extension water pipe supported upon at least one steerable drive tower;   steering means for steering said steerable drive tower;   drive means for driving said steerable drive tower, including at least one electric motor;   guidance means for controlling said steering means so that said steerable drive tower is moved along a preselected path, as said main boom travels over the field to be irrigated, thereby causing said corner span to pivotally move with respect to said main boom to cause said corner span to pivotally extend out into corner areas of the field and pivotally retract therefrom as said main boom travels through the field;   a span sensor positioned on said corner span for monitoring shape changes of said corner span;   control means connecting said span sensor and said electric motors on said last regular drive tower and said steerable drive tower for controlling the operation of said electric motors upon said span sensor sensing changes in shape of said corner span.   
     
     
       3. The irrigation system of claim 2 wherein said electric motor on said last regular drive tower is a variable speed electric motor. 
     
     
       4. The irrigation system of claim 2 wherein said electric motor on said steerable drive tower is a variable speed electric motor. 
     
     
       5. The irrigation system of claim 2 wherein said electric motors are variable speed electric motors. 
     
     
       6. The irrigation system of claim 2 wherein said span sensor is positioned on said corner span adjacent said steerable drive tower.